Many genetically encodable reporters have been developed to monitor spatio-temporal dynamics of specific enzymes in living cells. However, improved reporters are desired. For example, the Akt reporter “Aktus” (Sasaki et al., J. Biol. Chem. 278, 30945-51, 2003), requires overexpression of Akt to show signals in CHO cells, decreasing its applicability to study the regulation mechanism of endogenous Akt. The sensitivity of the Akt activity reporter “B Kinase Activity Reporter” (BKAR) (Kunkel et al., J. Biol. Chem. 280, 5581-87, 2005) is improved relative to Aktus, but its signal amplitude still limits its biological applications.
In addition, the art does not yet have enzymatic reporters for some enzymes. For example, there are no reliable methods available for measuring activity dynamics of JNK, one of the mitogen activated protein kinases (MAPKs), within subcellular compartments with high spatiotemporal resolution in living cells. Similarly, phosphatase activity reporters have not been described.
Thus, there is a continuing need in the art for sensitive and specific enzyme reporters, particularly genetically encodable reporters, which can be used to measure enzyme activities with high spatial and temporal resolution in vivo.